In the tropics, bats are active all year round, while in temperate areas many bats migrate or enter a period of torpor during winter, emerging again in September, and remaining active until April.

There are 90 species of bats in Australia, making up one-quarter of all mammal species. Most of these are insectivores that fly at night or twilight. Although often dwarfed in size and social behaviour by their larger, fruit-and-nectar eating cousins, these skilled fliers have their own fascinating stories to tell.

Microbats range in size from the tiny Little Forest bat, weighing in at 3.5-5 grams or about the same as a teaspoon of water, to the Ghost bat, which may be as long as 11 cm nose to tail. Most are forest dwellers, while others mass in caves, often in large numbers.

Bats have long since done what children the world over usually try once - using their arms to fly. They are the only mammals, apart from a few gliders, who have developed this capacity. These charming creatures occupy a niche abandoned by all but the night-flying birds, the period from dusk until dawn when insects are generally out in force. They are prey to few animals, making up a tiny portion of the diet of owls, some birds such as hawks, pythons in caves and snakes and goannas in trees.

Bat talk

Most bats navigate by echolocation. They emit high frequency pulses of sound through their mouth or nose which bounce off surfaces and objects around them. Bats pick up the echoes of these sounds with the aid of their extraordinary ears, and use this sonar signal to locate where they are and what is flying in front of them. The timing, loudness and direction from which the echo arrives at each ear indicates the direction and distance of the object.

A typical bat hunting for prey will produce 10 to 20 individual sounds per second. So precise is this sonar view of the world that bats can distinguish by size, shape and texture something as small as a mosquito. As the bat zooms in on its quarry the sounds may increase in frequency to around 200 sounds per second.

Some of the larger insect-eating bats produce echolocation sounds audible to humans, but for the most part bats seem to fly silently through the night. Bats also produce audible squeaks to communicate amongst themselves.

Some insects have picked up on bats' clever hunting strategy and turned it to their own use. Some species of moths have developed hairs on their wings that absorb the bats' sounds. Other moths in the families Noctuidae and Arctiidae have developed membranes that sense bats' echolocation and enable them to take evasive action, flying in a loop or dropping quickly out of the bat's flight path when it detects their presence.

Bats' wings are thinner and respond more quickly than birds' wings, making them capable fliers. Bats also possess hairs on the surface of their wings which let them sense the air flowing over their wings.

Feeding

Insect-eating bats dine on a delectable range of food from beetles and moths to ants, and bugs. The majority dine as they fly and are voracious feeders, eating around 50% of their bodyweight each night.

Some bats have even been utilised in pest control experiments, keeping boll moth numbers down in cotton plantations.

A familiar town-dweller found Australia wide is the Lesser Long-eared bat (Nyctophilus geoffroyi) which is often found catching moths and flying bugs around streetlights.

A familiar town-dweller found Australia wide is the Lesser Long-eared bat (Nyctophilus geoffroyi) which is often found catching moths and flying bugs around streetlights.

The Southern Myotis (Myotis macropus) or fishing bat specialises in aquatic foods, including aquatic insects and even small fish. They fly just above the surface of the water, sweeping the liquid with their feet and catching prey with their curved claws.

The Ghost bat (Macroderma gigas) has become even more specialised, and is one of a few bat species worldwide known to have turned on its own kind. The largest of the microbats, this white-furred cave dweller found across northern Australia also counts lizards and frogs among its prey, and uses its eyes as well as sonar to hunt.

Breeding

Microbats can form colonies from tens to tens of thousands during breeding season. Cave-dwelling females form particularly large nursing colonies, choosing a spot with relatively high temperature and humidity where they gather in their masses to breed. These caves are crucial to the species' survival and disturbances in the area can have dire consequences for the bats.

Females may give birth to one or two infants at a time. They nurse their young for six to eight weeks, during which time the infants cling to their mothers. Young bats have been known to nurse from other females in the colony.

Sleeping

Winter is an important time of year for cave-dwellers, when they most need to conserve energy. To do this, they enter a state of torpor, a semi-hibernation during which their temperature drops to the same temperature of the cave and they move very little. Forest dwellers may also spend much of their time in this voluntary shut down, explains Rob Gration, president of the Australasian Bat Society.

"They have the capability to virtually shut down their system at any time they need. Having said that I've been out in July when it's 3 degrees and seen them - they will occasionally wake up, have a drink and a top up feed," he says.

"People are probably quite often seeing bats without realizing it," adds Gration. Around streetlights in leafy suburbs what often seems like a moth at first glance may in fact be a small bat. Look out for fast flyers with longer wings than moths, he says.

Threats

The most significant threat to bats is habitat clearance, particularly the removal of the old forest wood where they roost in hollows or under the bark of trees.

"Most bats are tree hollow-dwelling and an enormous amount of woodland has been cleared in Australia and continues to be cleared," points out bat expert Terry Reardon from the South Australian Museum.

Others who live in caves can suffer if they are disturbed, particularly in the winter when arousal from torpor can cause them to lose critical fat reserves and die.

Some bats seem to have a knack for finding unusual places to sleep. Bats have been reported in exhaust pipes of vehicles, jackets hung up for the night or the inside of folded canvass chairs. Gould's Long-eared Bats (Nyctophilus gouldi) often choose to live in the abandoned nests of birds, while others such as the Little Pied bat, found in arid areas of New South Wales, may call an abandoned mine their home. The versatile Little Broad-nosed bat, which is found throughout most of northern Australia, can even be found under the metal caps of telephone poles.

"The Lesser Long-eared's are particularly notorious for being found in unusual spots," says Gration.

Bats can be fussy in their habits and a little disturbance may have drastic consequences. Horseshoe bats are particularly averse to flying over open ground. Reardon also points out that wind farms may claim bat lives, citing one wind farm which was responsible for the deaths of 4000 bats of eight different species.